Wireless digital networks, such as networks operating under the current Electrical and Electronics Engineers (IEEE) 802.11 standards, are spreading in their popularity and availability. Present antenna systems for wireless local area networks (WLAN), e.g., under IEEE 802.11 standards, can be categorized by two general types.
The first general type includes passive antennas. Passive antennas typically have no ability to actively alter, switch, or reshape their antenna pattern. Moreover, a passive antenna is usually connected to a radio access point, and thus its antenna pattern and coverage shape are fixed by the mechanical installation of the radio access point. In some cases, the mechanical installation may provide some flexibility in directing the antenna pattern to a desired coverage area (also known as “azimuth and elevation adjustment”), for example, by electrically adjusting mechanical or motorized mechanical mounts. Nevertheless, once the mechanical movement is fixed, the resulting antenna pattern and coverage area of the radio access point and the passive antenna combination usually does not change.
The other general type of antenna systems includes active antennas. Active antennas typically have the ability to electrically reshape the radiated pattern of the antenna, for example, by electrically switching the elements that are connected to the access point radio. The active antennas can further be categorized into two sub-types: diversity antenna arrays, and smart antenna arrays. In the case of diversity antenna arrays, the active element may be selected based on various methods, which may include received signal strength or communication error rates above and/or below a certain threshold. For example, in a radio access point having diversity antenna arrays, when a predetermined threshold is crossed, the radio will switch to another antenna of the radio access point. Typically, in the case of diversity antenna arrays, the antenna system is typically designed to provide the same coverage pattern from multiple passive antennas. Therefore, the antennas are simply switched one at a time to improve the radio communication link based on the diversity selection method.
By contrast, the other type of active antenna includes smart antenna arrays. The smart antenna arrays include an array of antennas or other radiating elements that can be switched to reshape the direction, pattern, and gain characteristics of the overall radiating structure. In the case of smart antenna arrays, the pattern and gain shaping selection can often be based on ways that are intended to dynamically reshape the antenna pattern to direct more signals toward the other side of the radio link. Because radio waves are reciprocal, dynamically reshaping the antenna pattern towards the opposite side of the radio link can improve the communication link quality in both the transmitting direction and the receiving direction.
The process generally described as directing radio signals toward the desired coverage area often is referred to as “pattern” or “coverage” management. Besides improving the radio link in the desired direction, pattern and coverage management can also be used to direct signals away from undesired directions for interference mitigation purposes and/or improved wireless security. For example, it may be desired that an office building provides WLAN signals only inside the office building with minimal WLAN signals available in the parking lot of the next building, which presumably is an unsecured area where network monitoring (“sniffing”) or active wireless network attacks (“hacking”) attempts can be more easily initiated against the private wireless network. This will become a problem for passive antennas, because passive antennas have no ability to reshape their antenna patterns to improve the signal in the desired coverage direction. Likewise, the above example can become problematic for active diversity antenna arrays as well, because active diversity arrays are simply a switched group of passive antennas, e.g., switching one passive antenna at a time and not in combination.
Smart antennas can be used for pattern and coverage management, but one problem with conventional smart antenna systems is that the selection methods are based on analysis of individual radio level, such as, a signal strength and an incoming signal direction, and not based on any high level coordination of multiple radios.
In a typical modern WLAN deployment, for network capacity reasons, it is not unusual to have many access points operating in close proximity to each other. The conventional smart antenna systems have the ability to drastically reshape the pattern of an individual radio and even to manage pattern shaping in real time to support multiple links in different directions, but these smart antenna systems do not have any ability to act in a coordinated fashion to achieve overall facility coverage and pattern management.